September 26, 2017
Early this September, Virginia Institute of Marine Science (VIMS) researchers Bob “JJ” Orth and David Wilcox and their colleagues at the Chesapeake Biological Laboratory (CBL) got a big surprise.
Each year, Orth and Wilcox review aerial photos of Chesapeake Bay to map the coverage of bay grasses, also called submerged aquatic vegetation (SAV), in our nation’s largest estuary. When they inspected photographs of the Patuxent River, they noticed something interesting: small patches of dark color near the Chesapeake Biological Laboratory’s research pier, which enters the Patuxent River off of Solomons Island. As they examined images from other parts of the Patuxent, they saw similar, often larger patches of what looked like bay grasses. Because bay grasses have not been seen off of the pier since the late 1960s, the VIMS researchers contacted their CBL colleagues Jeremy Testa, Lora Harris, and Walter Boynton, encouraging them to take a closer look.
The very next day, CBL technician Casey Hodgkins took a camera and jumped off the pier, swimming in and around the small patches that were, indeed, healthy beds of the SAV Ruppia maritima, commonly known as widgeon grass.
Interest in these small patches stems from the fact that SAV has not been seen off of the pier in decades. In fact, VIMS photographs going back to 1984, when their mapping project funded by the Chesapeake Bay Program began, have never indicated bay grass beds at CBL.
The decline of SAV in the Patuxent River was a typical story: increasing nutrient inputs from the watershed, primarily from human actions on land, fueled algal growth in the water that prevented light from reaching the bay grasses, which grow along the Bay’s bottom. These conditions also favored the growth of algae that grow on the leaves of the bay grasses themselves, further shading them from light. This loss of bay grasses was part of what spurred Senator Bernie Fowler to begin his annual “Wade-In” and draw attention to the nutrient obesity problems of the Patuxent River and the Chesapeake Bay.
In the early 2000s, Walter Boynton and Bob Stankelis attempted to replant the CBL shores with bay grasses. Sadly, this effort failed, primarily because the algae growing on the plant leaves, called epiphytes, smothered the leaves, especially during the warm months of the year. Bob Orth’s group at VIMS also attempted to grow eelgrass from planted seeds, but were also unsuccessful. It seemed that more time or further nutrient input reductions were needed to restore SAV.
Fast-forward to 2017: Large reductions in nutrients coming from the Bay’s large sewage treatment plants, a gradual reduction in the amount of nitrogen entering the Bay from the lands surrounding the Susquehanna River, and an extended period of moderate to low river flow appear to be leading to better conditions for the growth of bay grasses in parts of Chesapeake Bay. In 2015 and 2016, large grass beds appeared in many places around the middle part of the Bay, including near the mouth of the Patuxent River where the Chesapeake Biological Laboratory is located. These grass beds in the mainstem of the Bay appear to be the same species that was found off CBL this fall. Water clarity was indeed high over large regions of the middle Bay during summer and fall of these recent years. Could this be a sign of bay grass comeback?
The answer remains unclear. While recent water quality conditions have been improving, consistent with bay grass recovery across large swaths of the low-salinity, or less salty, regions of Chesapeake Bay, the trends in the mildly salty parts of the Bay—which includes the Patuxent River—have not been clearly up or down. The species of bay grass that appears to have colonized the Patuxent, widgeon grass, is known to be a patchy and ephemeral species, which appears for a few years and then disappears just as fast as it arrived if water quality degrades.
The Chesapeake Bay is always vulnerable to water quality declines when the weather causes high rates of precipitation and river flows that deliver nutrients to the tidal waters. While years with these high flows have been uncommon lately, it is inevitable that a period of high precipitation will return. But will the same level of river flow deliver the same amount of nutrients in the past? At least for the Susquehanna and Potomac Rivers, it appears that nutrients levels in many streams within the watersheds have declined, leading to lower nutrient inputs for a given flow. Only time will tell if this pattern will continue.
Scientists continue to study trends in bay grass coverage and the factors that control its growth, such as water clarity, nutrient inputs, and temperature. Chesapeake Biological Laboratory has recently launched a new monitoring system off of its pier that measures atmospheric conditions, water quality, temperature, and light availability in real-time—this new data stream will help connect future observations of bay grasses with the conditions of the water in both the near and far term.
Local citizens should keep a lookout as they swim, boat, and wander the shorelines of the Patuxent River and Chesapeake Bay, and contact Dr. Jeremy Testa (firstname.lastname@example.org) if they find something that looks like grass growing on the river bottom.